Holmesian fallacy

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A Holmesian fallacy (also Sherlock Holmes fallacy or process of elimination fallacy) is a logical fallacy that occurs when some explanation is believed to be true on the basis that alternate explanations are impossible, yet not all alternate explanations have been ruled out.

The fallacy is an appeal to omniscience and an informal fallacy.


[edit] Alternate names

  • far-fetched hypothesis
  • arcane explanation

[edit] Explanation

This fallacy usually occurs when someone uses the Holmes Method without being a superhuman genius. The Holmes Method is illustrated by the quote from the 1926 Sherlock Holmes short story "The Adventure of the Blanched Soldier":

When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.[1]

To apply this method, one must find explanations and eliminate them one by one. However, to draw a logical conclusion from this is fallacious, because both steps require omniscience:

  1. Find every possible explanation.
  2. Correctly disprove every possible explanation, except the true and undisprovable one.

As should be obvious, this is incredibly difficult, requires all knowledge of the situation, and may lead one to ridiculously improbable explanations.

[edit] Far-fetched hypothesis

Crop circles and other paranormal activity often fall into this fallacy. For example:

Look at that mutilated cow in the field, and see that flattened grass. Since the farmer is away and couldn't have done the deed, aliens must have landed in a flying saucer and savaged the cow to learn more about the beings on our planet.

Naturally, these are not the only explanations. Angry neighbors, rival farmers, predators (not the Schwarzenegger movie kind), undetonated ordnances from a past war (if applicable), and many other perfectly mundane probabilities exist that must be eliminated. Even assuming they are, there are myriads of other supernatural phenomena that could potentially explain the death of the cow and the flattening of the grass that would similarly need to be falsified before the conclusion of "UFOs" or "Aliens" can be accepted under this logic (for example, perhaps it was attacked by an avian cryptid. Perhaps it was struck down by [Insert Deity Here]. Perhaps it was possessed by ghosts or demons, causing the cow to burst as they departed its body. Perhaps it is evidence of an airborne biological weapons test by Monsanto, designed to kill all cattle and force America to eat GMO-fed meat. And so on. Ad nauseam infinitum.)

According to Aristotle in De Anima, the philosopher Thales of Miletus once said (paraphrased):

The lodestone has a soul because it moves iron. This proves that all things are full of gods.[2]

Thales failed to falsify all alternate explanations because he didn't know that magnetism existed. Similarly, we may be disproven by future discoveries.

[edit] Unfalsifiable explanations

Most often, the Holmes method leads people to explanations that are easy to find but difficult or impossible to falsify, such as god of the gaps and other supernatural entities with unknown properties. Often, people ignore the flaws in their preferred explanation.

Arthur Conan Doyle, the creator of Sherlock Holmes, ended up believing in spiritualism and fairies "using" the Holmes method.

[edit] Legitimate use

It is possible to grant provisional (scientific, not logical) assent to an explanation if it explains something better (or more simply) than all known alternatives. This isn't an absolute truth, merely the most probable one.

[edit] See also

[edit] External links

[edit] References

  1. Similar quotes appear in Chapter 6 of the 1890 Sherlock Holmes novel The Sign of the Four ("How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable. must be the truth?") and in the 1892 Sherlock Holmes story "The Adventure of the Beryl Coronet" ("It is an old maxim of mine that when you have eliminated the impossible, whatever remains, however improbable, must be the truth.")
  2. http://www.iep.utm.edu/thales/

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